Science Affliction #15

Going a bit of a different way with Science Affliction this week. All of the posts will be related to handedness and interesting scientific discoveries regarding the anomaly that left-handers make up such a relatively small portion of the population (about 10%). I’m afraid this post will come out a bit more like a research paper than “cool science news” so you may want to back away slowly and then run like hell.

The idea for the topic of this post came from a video from a few years back from one of my science heroes, James Watson. He did a TEDTalk where he talked mostly about his group’s discovery of DNA, but he also talks a bit at the end about what he’s interested in now, which is the genetic pre-disposition for diseases and disorders. That part of his talk starts at about 15 minutes, if you want to skip ahead. (I do recommend watching the whole video because Watson is a great example of a non-stereotypical scientist. He’s humble and funny, and very approachable.)

So, his point about the link between schizophrenia and left-handedness has support from more recent studies. Like most cutting edge science, there’s a lot of disagreement on that point. That got me thinking about the genetics of handedness in general, and why only 10% of the human population is left-handed.

1) Here’s an article that talks about the genetics of handedness. Basically, there’s one gene with two possible options, one says you’re right-handed and the other says you have a 50/50 chance of being either left or right handed. Only approximately 10% of humans are left-handed. This would tend to say that the heritability of left-handedness would be around 25%, which the numbers support.

3) One study went to the world of sports for an answer and determined that the reason for the left and right-handed balance in humans has to do with how much cooperation and competition we require in our society. In sports where competition is favored, the number of left-handers is larger than the population average. Their model accurately predicted percentages in many sports, but does that mean it works as an indicator for the population at large?

4) I’ve saved the best for last. This article from 2008 is probably the most balanced of the bunch, and proposes that the predisposition for right-handedness may have evolved along with our capability for speech. To me, this makes the most sense. Our brains have obviously adapted for some reason to favor one side of the brain over the other (more so than other animals like chimps that have so much genetic similarity to us) and there has to be an evolutionary reason for it that goes beyond our use of hands.

That’s all the left-handed links I have for you today. Hope you learned something interesting! I sure did.